Outdoor navigation and positioning have been widely deployed, including various global navigation-satellite-systems (GNSS) as well as various cellular systems. Indoor navigation and positioning often differs from outdoor navigation and positioning because the indoor environment may inhibit the reception of signals from satellites or cellular base stations. As a result, accurate and real-time indoor navigation and positioning may be difficult to achieve. Mobile devices (e.g., mobile station (STA) or simply STA in the IEEE 802.11 family of standards (hereinafter “802.11”)) may have mechanisms to access location information. Such a navigation device is herein referred to as a SET. GNSS (e.g., GPS) is an example of a mechanism that may be used by SETs to get location information. GNSS suffer from various problems, such as difficulty in receiving signals in certain areas (e.g., indoors as noted above) and responsiveness (e.g., a long turn-on time to location acquisition).
Assisted GNSS (A-GNSS) was developed to augment GNSS and resolve some of the previously discussed GNSS shortcomings A-GNSS supplements the generally satellite-signal-only GNSS mechanism with additional data or services. A-GNSS may include supplemental information including: providing a mobile device with precise time; providing satellite data (e.g., orbital data or almanac); signal correction; or position computation based on a provided satellite signal snapshot from the mobile device, among others. AGPS is a variant of A-GNSS. Other examples of A-GNSS may include the use of cellular-based positioning system (e.g., Enhanced cell-id, observed time difference of arrival (OTDOA), enhanced observed time difference (E-OTD)) and wireless local area network (WLAN) access point (AP) received signal strength indication (RSSI).